A superconducting magnet device that generates a high magnetic field using a superconducting coil in a superconducting state has conventionally been known. For example, JP 2007-194258 A discloses a superconducting magnet device including a superconducting coil, a cryogenic container containing the superconducting coil and liquid helium, a heat shield housing the cryogenic container, a vacuum case housing the heat shield, and a refrigerator, mounted on the vacuum case, for refrigerating the heat shield and the superconducting coil. The refrigerator includes a first cooling stage for cooling the heat shield via a heat transfer member, a second cooling stage for cooling the superconducting coil with helium, and a refrigerator body fixed to the vacuum case with the first cooling stage in thermal contact with the heat shield via the heat transfer member. In many cases, the refrigerator body is fixed to the vacuum case by fastening members such as bolts.
To maintain the refrigerator of the superconducting magnet device, the fastening members are removed and the refrigerator is pulled out of (removed from) the vacuum case.
For the superconducting magnet device as disclosed in JP 2007-194258 A, it is difficult to remount the refrigerator on the vacuum case with the first cooling stage in suitable thermal contact with a radiation shield after maintenance or replacement of the refrigeration unit. Specifically, the first cooling stage in contact with the radiation shield at a high contact pressure creates a preferable thermal contact between the first cooling stage and the radiation shield. However, an excessive fastening force applied by the fastening member might damage the first cooling stage. In contrast, an insufficient fastening force applied by the fastening member results in insufficient thermal contact between the first cooling stage and the radiation shield, which leads to failure of sufficiently cooling the radiation shield. The fastening member thus needs to be fastened such that a fastening force applied by the fastening member is not too large but not too small. It is however difficult to fasten the fastening member so as to produce a fastening force within such a preferable range.
The aforementioned problem may also arise in a device that does not include liquid helium and a helium tank storing the liquid helium, that is, a superconducting magnet device that cools a superconducting coil not by liquid helium but by a second cooling stage via a member, such as a plate having high thermal conductivity.